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I'm just a user like you, but from the description, it sounds like without global buffers you can't use the Scatter operation (random access write). It also sounds like it implies that you can't "gather" (random access read) either; however, I know that not to be the case with R600. This may be an oversimplified answer to your question.
so r600 has scatter and gather operations implemented in a different way than the r670 which implement these operations using global buffers. Is it correct?
Thanks a lot for helping me to understand.
R600 does not support scatter, period, as far as I know.
I have a 2900XT (R600) and I have been told by AMD that it does not support scatter (it also does not support double precision, obviuosly). It is a hardware limitation.
I only tried to deduce the correlation from the statement:
The Global Buffer relaxes this limitation by providing applications with the flexibility to read from and write to arbitrary locations in input buffers and output buffers respectively
which makes it sound like they are talking about gather and scatter using global buffers.
ALSO, I believe that the "HWGuide.doc" talks about this some, indicating that "stream" operations are much faster than "scatter/gather" operations since "stream" operations are cached while "scatter/gather" operations use global buffers.